Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$223.32	8.544%	$242.4005	$242.40	$242.40	$242.40
Purchase #2	$78.81	11.667%	$88.0048	$88.00	$88.00	$88.00
Purchase #3	$123.52	6.766%	$131.8774	$131.88	$131.90	$131.90
Purchase #4	$59.54	5.134%	$62.5968	$62.60	$62.60	$62.60
Purchase #5	$12.32	3.225%	$12.7173	$12.72	$12.70	$12.70
Purchase #6	$45.72	12.378%	$51.3792	$51.38	$51.40	$51.40
Purchase #7	$164.63	12.840%	$185.7685	$185.77	$185.75	$185.80
7 purchase totals =	$707.86		$774.7445	$774.75	$774.75	$774.80